Voltage control



y 25, 1954 R. H. HAGOPIAN 2,679,593

VOLTAGE CONTROL Filed Mafch 26, 1949 W I T NESSESf 'INVENTOR &47%/ Richard H.Hogopic|n.

Patented May 25, 1954 UNITED STATES PATENT OFFICE VOLTAGE CONTROL Richard H. Hagopian, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania- Application March 26, 1949, Serial No. 83,540

15 Claims. 1

This invention relates to controls for maintaining constant voltages in electrical circuits, and relates more particularly to controls for automatically maintaining the output voltages of radio frequency generators, constant.

Radio frequency generators are used in industrial heating systems, such as dielectric heating systems, for heating work articles. Difierent articles heated in succession offer difierent loads, and load changes occur in the articles during the heating thereof due to changes in their electrical characteristics. Load increases, above normal, cause corresponding reductions in the radio frequency output voltages, and load decreases, below normal, cause corresponding increases in the radio frequency output voltages. It is desirable for reasons of efficiency and of quality control of the work articles, that the radio frequency output voltages be maintained substantially constant regardless of load changes, and is accomplished by this invention.

In one embodiment of the invention, a rectifier rectifies a sample of the radio frequency output voltage to be maintained constant, and supplies it to the cathode of a first amplifier tube, the control grid of which is normally biased to near cut-off by a resultant of the rectified voltage and the voltage from a contant voltage bias supply. A first relay has its energizing winding connected in the plate circuit of the amplifier tube, and is energized by an increase in plate current caused by an increase in the radio frequency voltage, and actuates a control to decrease the radio frequency voltage to normal.

The plate of the amplifier tube is direct-connected to the control grid of a second amplifier tube which has the energizing winding of a second relay connected in its plate circuit. The increase in the plate current of the first amplifier tube caused by the increase in radio frequency voltage, causes the second amplifier tube to be biased beyond cut-oif.

A decrease in radio frequency voltage below normal, causes the first amplifier tube to be biased to cut-off and this causes a zero bias on the grid of the second amplifier tube causing it to draw sufficient plate current to energize the second relay which then actuates a control to increase the radio frequency voltage to normal.

A feature of the invention is that the sensitivity of its control may be easily adjusted over a wide range by varying the ratio of the bias voltage from the constant voltage source, to the bias voltage provided by the rectifier, from the radio frequency voltage. i

An object of the invention is to maintain constant voltages in electronic circuits.

Another object of the invention is to maintain the output voltage of a radio frequency generator, constant.

Another object of the invention is to provide a relatively inexpensive, automatic voltage control for a radio frequency generator.

Another object of the invention is to provide an automatic voltage control for a radio frequency generator, the sensitivity of which can easily be adjusted over a wide range.

The invention will now be described with reference to the drawing which is a circuit schematic of one embodiment of the invention as used with a radio frequency generator.

The push-pull connected, oscillator tubes II! have their control grids connected to the grid inductor II, and have their plates connected to the tank inductor l2 and to the load l3, the center of the inductor I2 being connected to the positive terminal of a suitable plate voltage supply source, the negative terminal of which is grounded as is conventional. The load l3 may, by way of example, be a conventional dielectric heating load.

The tank inductor I2 is connected through the series-connected, voltage dividing capacitors I 4 to ground, the centerpoint connection of the capacitors being connected to the plate of the diode, rectifier tube l5, which also is connected through the potentiometer IE to ground. The cathode of the tube [5 is connected through the resistor H to ground.

The slider I8 of the potentiometer I6 is connected through the resistor l9 to the cathode of the amplifier tube 20. The constant voltage, b1- as voltage supply source 2| has its negative terminal connected to the control grid of the tube 20, and has its positive terminal connected to ground. The grid resistor 22 is shunted across the source 2|.

The plate and the screen grid of the tube 20 are connected together and to one side of the relay winding 23, the other side of which is connected through the series-connected potentiometer 24, the resistor 25 and the filter choke 26 to the positive side of the rectifier 21. The negative side of the rectifier 21 is connected to the slider l8 of the potentiometer l6, and through the resistor Hi to the cathode of the tube 20.

'The rectifier 21 consists of the four selenium rectifier elements 28 connected in a conventional bridge circuit to the secondary winding 29 of the transformer 30, the primary winding. 3| of which is connected to a 110 volt, 60 cycle, alternating current source. The filament windings 32 and 33 may be used to energize the filaments of the tubes l and 20 respectively. The capacitors 34 are filter capacitors, the resistor 35 is a load resistor and the tube 36 is a voltage regulator tube, for the rectifier 21.

The slider 31 of the potentiometer 24 is connected to the control grid of the tube 38. The plate and the screen grid of the tube 38 are connected together and to one side of the relay winding 39, the other side of which is connected through the series-connected resistors 49 and 4|, and the filter choke 42 to the positive side of the rectifier 43. The negative side of the rectifier 43 is connected to the cathode of the tube 38, which also is connected to the junction point of the series-connected potentiometer and resistor 25. The positive terminal of the rectifier 21 is connected by the wire 48 to the negative terminal of the rectifier 43.

The rectifier 43 consists of the four selenium rectifier elements 48 connected in a conventional rectifier bridge circuit to the secondary winding 44 of the transformer 45, the primary winding 48 of which is connected to the 110 volt, 60 cycle source. The filament winding 4'! of the transformer may be used to energize the filament of the tube 38.

The capacitors 49 are filter capacitors, the resistor 59 is a load resistor, and the tube 51 is a voltage regulator tube, for the rectifier 43.

The filaments of the oscillator tubes H] are connected together and to the secondary winding of the filament transformer 54, the primary winding of which has one end connected to one end of the auto-transformer winding 55, and has its other end connected to the slider 55 of the winding 55. The ends of the winding 55 are connected to the 110 volt, 60 cycle source.

The slider 55 of the auto-transformer Winding 55 is mechanically connected to the armature of the electric motor 58 in such a way that when the armature rotates in one direction it moves the slider 56 along the winding 55 to increase the voltage supplied to the filament transformer 54, and when it rotates in the opposite direction, it moves the slider along the winding 55 to decrease the voltage supplied to the filament transformer.

The plungers of the relay windings 23 and 39 are connected together by the cross-bar 59 of insulating material which has supported therefrom, the relay armature 6!.

The contacts 62 and 83 are each connected to one side of a pair of field windings 64 and 55'. The other side of each field winding is commonly connected to the armature of the motor 58. A power source 55 is connected between the other side of the armature of motor 58' and a contact on the relay armature 6|. This is a conventional motor reversing circuit in which, when relay armature (it touches contact 53, a circuit is completed for the field winding 64, the armature of motor 58 and the power source 66 thereby causing the motor 58 to rotate in one direc-' tion. When relay armature Bl touches contact 52, field winding 65 is placed in series with the armature of motor 58 and the power source 86 causing motor 58 to rotate in the other direction.

The rectifier tube l5 may be a 6X5, and each of the tubes 29 and 38 may be a 6L6. p v

Normally the fixed bias voltage which may be 100 volts, from the bias supply source '2! ex- 4 ceeds the bias voltage supplied from the rectifier tube l5 by about 14 volts. With about 140 volts from the rectifier 2'! on the plate of the tube '29, it draws about 10 milliamperes of plate current which is too small to cause the relay winding 23 to pull in its plunger. It is sufficient however to provide a bias to about -12 volts on the control grid of the tube 38 through the voltage drop in the potentiometer 24. The resulting plate current drawn by the tube 38 from its rectifier 43 is too small to cause the relay winding 39 to -pull in its plunger. Thus as long as the output voltage of the oscillator tubes I9 remains constant, the relay armature Bl is spaced from its associated contacts 52 and 83, and the motor 58 does not operate.

Should the radio frequency voltage increase about 10% the plate current of the rectifier tube 15 will increase sufficiently to cause the effective bias on the control grid of the tube 28 to decrease to zero, and to cause its plate current to increase to about milliamperes. This increase in plate current causes the relay winding 23 to pull in its plunger, causing the relay armature 5| to strike the contact 53. This causes the motor 58 to be energized to rotate in a direction to move the slider 56 of the auto-transformer so as to decrease the voltage supplied by it to the filament transformer thereby reducing the voltage applied to the filaments of the oscillator tubes, and reducing the radio frequency output voltage and restoring it to normal, following which the relay winding 23 releases its plunger, and the motor 58 stops.

The increase in the plate current of the tube caused by the increase in the radio frequency voltage, also causes an increased voltage drop in the potentiometer 24 causing the tube 38 to be biased beyond cut-off so that there is no possibility of the relay winding 39 being energized.

A decrease in the radio frequency voltage of about 10% below normal, will cause the plate current of the rectifier tube I5 to decrease, and

- this will cause the effective bias voltage on the control grid of the tube 28 to increase to its cut-off voltage of about 30 volts. With the tube 29 biased ot cut-off, the voltage on the control grid of the tube 38 becomes zero, causing, with a plate voltage of about volts, its plate current to increase to about 50 milliamperes. This causes the relay winding 39 to become energized sufficiently to pull in its plunger, causing the relay armature iii to strike the contact 52. This, in turn, causes the motor to adjust the slider 55 of the auto-transformer Winding 55 in a direction to increase the voltage supplied through the filament transformer 54 to the filaments of the oscillator tubes l5, causing the radio frequency output voltage to increase back to normal at which time the relay winding 39 releases its plunger, and the motor 58 stops.

Should the radio frequency voltage become zero at any time, the tube 29 will be biased to cut-off. If the radio frequency voltage should increase greatly above normal, the resulting high plate current drawn by the tube 29 would result in an appreciable voltage drop through its cathode resistor l9, which will tend to reduce the plate current.

The sensitivity of the control may be increased or decreased by increasing or decreasing by adjustment of the potentiometer 15, the ratio of the grid bias voltage supplied from the rectifier to that supplied by the bias supply source 2|.

I claim as my invention:

1. An automatic voltage control for an alternating current generator, comprising a rectifier connected to the generator; an electron tube having a control grid, a cathode and an anode; means for varying the voltage of said generator; means including said rectifier for normally biasing said grid negatively with respect to said cathode, for decreasing the negative bias upon an increase in the voltage of the generator, and for increasing the negative bias upon a decrease in the voltage of the generator; an anode voltage supply source; relay means connected to said anode and to said source for adjusting said voltage varying means to decrease the voltage of the generator upon an increase in the anode current of said tube caused by a decrease in said negative bias; a second electron tube having a control grid, a cathode and an anode; means for so connecting said last mentioned grid and cathode to said first mentioned anode and to said source that said last mentioned grid is normally biased negatively with respect to said last mentioned cathode, and a decrease in the anode current of said first mentioned tube will cause said last mentioned grid to be biased less negatively with respect to said last mentioned cathode, and means including relay means connected to said anode of said second tube for adjusting said voltage varying means to increase the voltage of the generator upon an increase in the anode current of said second tube caused by a decrease in the anode current of said first mentioned tube.

2. An automatic voltage control as claimed in claim 1, in which the second mentioned means includes a source of constant voltage.

3. An automatic voltage control as claimed in claim 2, in which means is provided for varying the ratio of the voltage from the constant voltage source to the voltage from the rectifier.

4. An automatic voltage control for an alternating current generator, comprising an electron tube having a control grid, a cathodeand an anode; a rectifier having an anode connected to said generator and to said cathode, a bias voltage supply source having its negative side connected to said grid and having its positive side connected to said cathode; an anode voltage supply source for said tube; relay means connected to said tube anode and to said last mentioned source; means for varying the voltage of the generator; means actuated by said relay means for adjusting said voltage varying means for decreasing the voltage of the generator upon an increase in the anode current of saidtube; 'a second electron tube having a control grid, a cathode and an anode; means for so connecting said last mentioned grid and cathode to the anode of said first mentioned tube and to said last mentioned source that the last mentioned grid is normally biased negatively with respect to said last mentioned cathode, and that a decrease in the anode current of the first mentioned tube will cause the last mentioned grid to be biased less negatively with respect to the last mentioned cathode, and means including relay means connected to the cathode of the second tube for adjusting said voltage varying means to increase the voltage of the generator upon an increase in the anode current of the second tube caused by a decrease in the anode current of the first mentioned tube.

5. An automatic voltage control as claimed in 6 claim 4 in which means is provided for varying the ratio of the bias voltage provided by said bias voltage supply source to that provided by said rectifier.

6. An automatic voltage control for an alternating current generator, comprising first and second electron tubes, each having a control grid, a cathode and an anode; means normally biasing the grid of said first tube negatively with respect to its cathode; means responsive to voltage variations of the generator for inversely varying the negative bias voltage on the grid of the first tube; an anode voltage supply source connected to the anode of said first tube; means so connecting the grid of said second tube to the anode of the first tube, and the cathode of said second tube to said supply source, that the grid of the second tube is normally biased negatively with respect to its cathode, and that decreases in the anode current of the first tube will cause the grid of the second tube to be biased less negatively with respect to its cathode, and means including means connected to the anodes of said tubes for decreasing the voltage of said generator upon an increase in the anode current of said first tube and for increasing the voltage of said generator upon an increase in the anode current of said second tube.

'7. An automatic voltage control for an alternating current generator, comprising first and second electron tubes, each having a control grid, a cathode and an anode; means including a direct current source of constant voltage for normally biasing the grid of said first tube negatively with respect to its cathode; means including a rectifier connected to said generator for varying the negative bias voltage on the grid of said first tube inversely proportional to voltage variations of the generator; an anode voltage supply source connected to the anode of said first tube; means so connecting the grid of the second tube to the anode of the first tube, and the cathode of said second tube to said anode voltage supply source, that the grid of the second tube is normally biased negatively with respect to its cathode, and that a decrease in the anode current of the first tube will cause a decrease in the negative bias on the grid of the second tube, and means including means connected to the anodes of said tubesfor decreasing the voltage of the generator upon an increase in the anode current of the first tube, and for increasing the voltage of the generator upon an increase in the anode current of the second tube.

8. An automatic voltage control for an alternating current generator as claimed in claim '7, in which means is provided for varying the ratio of the bias voltage provided by the constant voltage source to that provided by the rectifier.

9. An automatic voltage control for an alternating current generator, comprising a rectifier having a cathode and an anode connected to said generator; an electron tube having a control grid, a cathode and an anode; means connecting said tube cathode to said anode of said rectifier; a source of constant voltage having its negative side connected to said tube grid, and having its positive side connected to said tube cathode; an anode voltage supply source; relay means connected to said last mentioned source and to said tube anode; means actuated by said relay means for decreasing the voltage of said generator upon an increase in the anode current of said tube; a second electron tube having a control grid, a cathode and an anode; means connecting said 7. last mentioned cathode to said anode voltage supply source; means including a resistor connecting said last mentioned grid to said anode of said first mentioned tube; an anode voltage supply source for said second tube; relay means connected to said second tube anode and to said last mentioned source, and means actuated by said last mentioned relay means for increasing the voltage of said generator upon an increase in the anode current of said last mentioned tube.

10. An automatic voltage control as claimed in claim 9, in which the means connecting the cathode of the first mentioned tube to the anode of the rectifier includes a variable resistor ad justable for varying the sensitivity of the control.

11. An automatic voltage control for an electrical circuit, comprising first and second electron tubes, each having a control grid, a cathode and an anode; means normally biasing the grid of said first tube negatively with respect to its cathode; means responsive to voltage variations in said circuit for inversely varying the negative bias voltage on the grid of said first tube; an anode voltage supply source connected to the anode of said first tube; means so connecting the grid of said second tube to the anode of said first tube, and the cathode of said second tube to said anode voltage supply source, that the grid of said second tube is normally biased negatively with respect to its cathode, and that decreases in the anode current of said first tube will cause the grid of said second tube to be biased less negatively with respect to its cathode, and means including means connected to the anodes of said tubes for decreasing the voltage in said circuit upon an increase in the anode current of said first tube, and for increasing the voltage in said circuit upon an increase in the anode current of said second tube.

12. An automatic voltage control as claimed in claim 11, in which the means normally biasing the grid of said first tube negatively with respect to its cathode, includes a source of constant voltage.

13. In control apparatus for controlling a motor in response to the magnitude of an input signal relative to a predetermined value for that signal, the combination including a first tube having a cathode, an anode and a grid, a second tube having an anode and a grid, a source of bias voltage connected between a cathode and grid of said first tube, a control circuit connected to operate said motor, a first relay means in the anode circuit of the first tube connected to said control circuit to operate the motor in a first direction, a second relay means in the anode circuit of the second tube and connected to said control circuit to operate the motor in a second direction, said source of bias voltage being sufficient to bias the first tube such that its anode current is not sufiicient to operate the first relay means when the value of the input signal is below said predetermined value, but said source ofbias voltage not being sufficient to so bias the first tube when the input signal value is above said predetermined value, a resistor in the anode circuit of the first tube, said resistor having an intermediate electrical connection point, a connection between the grid of the second tube and the intermediate point of said resistor. the value of said resistor being chosen to furnish a bias to the second tube such that its anode current is not sufiicient to operate the second relay means when the first tube is conducting due to the input signal being above said predetermined value, but said resistor having a value sufilcient to operate the second relay means when the first tube is not so conducting.

14. In control apparatus including a relay member having a pair of operating coils and connected to suitable control apapratus for controlling a variable parameter in response to an input signal corresponding to the controlled condition of said parameter, the combination including a first tube having an anode, a cathode and a grid, a resistor in the anode circuit of the first tube, said resistor having an intermediate point provided for making an electrical connection to said resistor, a second tube having an anode and a grid, an electrical connection between the grid of the second tube and the intermediate point of said resistor, each of said coils being respectively placed in the anode circuit of one of the tubes, 2:. source of bias voltage connected between the grid and cathode of the first tube, and connections to the grid of the first tube and adapted to receive said input signal.

15. In relay control apparatus which is responsive to an input signal corresponding to a condition of a controlled voltage, the combination including a first discharge device having an anode, a cathode and a control electrode, a second discharge device having an anode and a control electrode, a resistor in the anode circuit of the first tube, said resistor having a point provided thereon for making an electrical connection to said resistor, a connection between thecontrol electrode of the second discharge device and said point on said resistor, relay control means in the respective anode circuits of each discharge device, a source of bias voltage connected between the control electrode and cathode of the first discharge device, and connections to the control electrode of the first discharge device to receive said input signal.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,942,587 Whitman Jan. 9, 1934 2,175,694 Jones, Jr. Oct. 10, 1939 2,297,800 Read Oct. 6, 1942 2,387,544 Usselman Oct. 23, 1945 2,429,771 Roberts Oct. 28, 1947 FOREIGN PATENTS Number Country Date 505,500 Great Britain May 11, 1939 2,519,247 Great Britain Aug. 15, 1950 

